The present invention relates to a line printer. More specifically, the invention relates to an impact line printer which can maintain a high printing speed irrespective of variations in the types of printing fonts used on the type carrier.
Although type carriers may commonly be print bands, print drums, print trains and print chains and the like, a conventional impact line printer will be described with reference to a print band.
In one known printer, the print band incorporates 384 characters on one circumference, and contains 8 sets of 48 characters, 6 sets of 64 characters, 4 sets of 96 characters or 3 sets of 128 characters. A second known type of conventional line printer incorporates a print band containing 240 characters on one circumference, with 8 sets of 30 characters, 5 sets of 48 characters, 4 sets of 60 characters, or 2 sets of 120 characters.
It is also generally known to store in a read only memory (ROM) within the line printer an array of data corresponding to the sequence of type characters on the print band or to write and store in a Universal Character Set Buffer (UCSB) within the line printer an array of type character data transferred from the channel of a computer system to which the line printer is connected.
When using a ROM, it is necessary to replace the memory by a new one every time the print band is changed. If a UCSB is used, however, it is not necessary to replace the memory even when the print band is changed, but it is only necessary to transfer from the computer to the UCSB a type data array corresponding to the type characters on the new print band.
The size of the data array thus transferred from the computer to the UCSB depends upon the type of line printer to be connected. For example, 240 bytes are transferred for a line printer having a print band including 240 type characters, and 384 bytes are transferred for a line printer having a print band including 384 type characters. The controlling computers in available line printers, are usually not designed for use with both 240-character and 384-character line printers, but will only transfer either 240 or 384 characters to the line printer depending on the computer software. That is, a computer designed for use with a 240-character line printer can only transfer data corresponding to a 240-character print band. The size of the transferred type-character data array will always be constant unless the software for controlling the computer is modified. It is sometimes desirable in a system using a 240-character print band to replace the line printer by a new line printer employing 384 type characters on one circumference of the print band. However, in a system in which a type character data array is transferred from a computer to the UCSB within the line printer, it is impossible to merely replace the line printer by a new one due to the different number of type characters on the print bands of the two line printers, because there exists a problem that the computer software must then be modified as described above to change the size of the type character data array to be transferred.